Semiconductor integrated circuits designs and manufacturing techniques continue to evolve. Great progress has been made over the past generation in all phases of integrated circuit manufacturing so as to improve reliability of the finished products. Reliability of integrated circuits is of paramount importance to all concerned: the manufacturer, the OEM customer, and the end used. Indeed, in some "mission critical" applications, such as medicine or extra terrestrial applications, reliability of such circuits can be a matter of life and death. Even in more pedestrian applications, circuit failures lead to wasted time and expense, not to mention erosion of the manufacturer's reputation.
Although, in general, reliability of integrated circuits has become very high, the relentless push toward higher levels of integration, while maintaining high levels of reliability, presents an ongoing challenge. Part of the integrated circuit manufacturer's quest to improve reliability involves failure analysis--the analysis of failed parts in order to determine what caused the failure. Most manufacturers have extensive failure analysis departments, staffed by engineers and other professionals who are skilled in this specialty. Traditional methods of failure analysis include the following: Applying selected voltages to circuit inputs and examining selected output voltage levels, either through the use of a functional tester, mechanical probing system, or the use of an electron beam detection system. Another known method of failure analysis is to apply selected voltages at certain pins and measure the current that the IC draws in response. Another method involves applying selected currents at certain inputs and measuring the voltage levels or, applying selected voltages to predetermined pins and looking for "hot spots" on the integrated circuit ("IC") through either emission microscopy or infrared detection systems.
A primary disadvantage or limitation of known failure analysis methodologies is that they are limited to the use of electrical stimuli and the responses under examination are limited to electrical responses, photo emissions, or infrared emissions. When electrical stimulus is used, the response is limited to the output pins of the IC which in turn requires the use of additional hardware to detect the responses. This hardware is usually referred to as a device under test (DUT) board. The DUT board itself can introduce unwanted responses or affect the device responses in ways that can confuse the tester/failure analysis tool. In other words, the DUT testing equipment itself can corrupt the failure analysis. Where emission microscopy or infrared methods are used, the IC must have the suspect circuit exposed so that the emission microscopy or infrared systems can detect the hot spots. This typically requires decapping or some type of deprocessing of the IC in order to expose the circuit. These steps are time consuming and can themselves introduce defects into the IC which essentially renders the entire failure analysis suspect, if not useless.
Accordingly, it would be desireable to be able to identify and detect defects without the use of traditional DUT boards, or without going through all of the traditional electrical tests such as continuity, functional or other type of DC tests. Additionally, it would be desirable to be able to detect defects in ICs that are not detectable using traditional testing techniques such as those described above.